This invention relates to methods of and apparatus for wrapping, and more particularly to a method of and apparatus for wrapping palletized loads.
The invention is especially concerned with tightly covering loaded pallets with plastic shrouds, such covering being useful to reduce palletizing costs, to contain the load on a pallet, to discourage theft and pilferage, to improve outdoor weatherability, to provide a visual coding system for inventory control by using color additives in the plastic film, etc. Generally there have been two basic systems for effecting such a covering operation, which may be broadly classified as (1) stretch systems and (2) shrink systems. In the stretch systems as heretofore employed, plastic film from a roll or rolls thereof has been wrapped around the load under tension and sealed, the film then shrinking on the load. A problem with these prior stretch systems has been that the wrapping with film from a roll or rolls does not per se provide a covering for the top of the load, and, if a top cover is required, separate and usually manual operations are required to provide a top cover; e.g., a top cover is draped over the load, and film is wrapped around the sides of the top cover to anchor it in place. In the shrink systems as heretofore employed, generally a cover of heat-shrinkable plastic film is applied over the load, the cover being heated (as by conveying the loaded pallets with the covers thereon through a shrink tunnel or oven, or by means of a heater ring surrounding the load and traversed vertically relative to the load. Problems involved with these shrink systems are cost (cost of shrink film and cost of energy for heating), and, in many instances, impracticability or impossibility of heating; e.g., heating of the product on the pallet may be impractical or dangerous, or use of a heating device may be impractical or dangerous in a particular environment. For example, use of a heating device in a food freezer plant or an air-conditioned production area may be impractical, and use of a heating device in an explosive atmosphere would be dangerous. Also, shrink systems are impractical in cases where the load consists of a product packaged in bags of polyethylene or other heat-sealable material since the wrapper may become heat-sealed to the bags.